On Hopf bifurcation in non-smooth planar systems

Andronov, 1959 Bautin, 1952, On the number of limit cycles which appear with the variation of coefficients from an equilibrium position of focus or center type, Mat. Sb. (N.S.), 30, 181 Coll, 2001, Degenerate Hopf bifurcation in discontinuous planar systems, J. Math. Anal. Appl., 253, 671, 10.1006/jmaa.2000.7188 di Bernardo, 2008 Du, 2008, Bifurcation of periodic orbits in a class of planar Filippov systems, Nonlinear Anal., 69, 3610, 10.1016/j.na.2007.09.045 Filippov, 1988 Gasull, 2003, Center-focus problem for discontinuous planar differential equations, Internat. J. Bifur. Chaos Appl. Sci. Engrg., 13, 1755, 10.1142/S0218127403007618 Han, 2006, Bifurcation theory of limit cycles of planar systems, 10.1016/S1874-5725(06)80008-8 Kunze, 2000 Küpper, 2001, Generalized Hopf bifurcation for non-smooth planar systems, Philos. Trans. R. Soc. Lond. Ser. A Math. Phys. Eng. Sci., 359, 2483, 10.1098/rsta.2001.0905 Li, 2003, Hilbert's 16th problem and bifurcations of planar polynomial vector fields., Internat. J. Bifur. Chaos Appl. Sci. Engrg., 13, 47, 10.1142/S0218127403006352 Liu, 2009, Hopf bifurcation for non-smooth Liénard systems, Internat. J. Bifur. Chaos Appl. Sci. Engrg., 19, 2401, 10.1142/S0218127409024177 Zou, 2006, Generalized Hopf bifurcation for planar Filippov systems continuous at the origin, J. Nonlinear Sci., 16, 159, 10.1007/s00332-005-0606-8